1. Field of the Invention
The present invention relates to a sound motion picture camera.
2. Description of the Prior Art
At present, there is commercially available such type of film for use in motion picture camera which not only optically records image information but also magnetically records sound information on one and the same film. This type of film is generally called "sound film". One example of such type of film is a motion picture film sold by Eastman Kodak Company under the trade name "Sound Movie Film". As to this sound film, a detailed description has been made in U.S. Pat. No. 3,858,968 assigned to Eastman Kodak Company.
As seen from the above mentioned patent specification, this sound film of Eastman Kodak Company is formed by adding a strip of magnetic recording material along one side edge on one surface of a conventional silent film. This film is encased in a cassette. The cassette with the film contained therein is inserted into the cassette-receiving chamber of a camera to use the film. The sound film cassette has an opening for exposure and an opening for sound recording provided on the body of the cassette at two different positions. Within the body of the cassette, there are disposed coaxially a supply spool and a take-up spool. The sound film contained in the cassette is reeled up onto the take-up spool from the supply spool passing through the opening for exposure and the opening for sound recording.
Various types of sound motion picture cameras adapted for such sound film, are also known and commercially available. For example, mention may be made of U.S. Pat. No. 3,880,504, U.S. Pat. No. 771,864, U.S. Pat. No. T 920,009 (Defensive Publication) and U.S. Pat. No. 3,825,327. These known sound motion picture cameras are provided with some particular elements and devices which silent motion picture cameras conventionally used for a long time do not have. A sound motion picture camera is distinguished from a silent motion picture camera in that for the former there are additionally provided at least two devices, that is, a sound recording circuit device comprising a magnetic head for magnetically recording sound information on the magnetic recording material of the sound film and a film feeding device for transporting the sound film at a substantially constant speed directing it to the magnetic head.
At a position correctly aligned with the above mentioned image recording location in the cassette-receiving chamber where the opening for exposure of the cassette is to be located when the sound film cassette is properly loaded into the chamber, there are disposed an image forming device of the sound motion picture camera and the first film feeding device which engages with the sound film to intermittently transport it toward the opening for sound recording. Also, at a position correctly aligned with the above mentioned sound recording location in the chamber, the camera has the magnetic head of the sound recording circuit device and the second film feeding device which engages with the sound film at the opening for sound recording so as to transport the film at a substantially constant speed relative to the magnetic head.
Thus, within the sound motion picture camera loaded with the sound film cassette, recording of image information on the loaded film is effected at the position of the opening for exposure through the image forming device and recording of sound information associated with the image information is effected at the position of the opening for sound recording on the magnetic recording material applied to the same film through the magnetic head.
Image information and sound information associated with each other and recorded together on one and the same sound film are shifted from each other by a given distance with respect to the position of the recorded information on the film. This distance from the image information to the sound information on one and the same sound film is standardized to correspond to about eighteen picture frames for all such sound films manufactured by different film manufacturers. Therefore, the information recorded on the sound film may be reproduced by using a moving picture projector of any manufacturer. The standardization of shift distance from image information to sound information assures of matching of image to sound without distinction of manufacturer of projector to be used. However, on the other hand, in view of the camera side, this requires a precise feeding of film within a sound motion picture camera. The length of film segment existing between a part of the film carrying image information recorded thereon and a part of the film carrying sound information recorded thereon should be maintained always approximately constant. In other words, the speed at which the first film feeding device intermittently transports the film for a unit of time and the speed at which the second film feeding device substantially constantly transports the film for the same unit of time should be maintained constant always. This is very difficult to actually attain. For example, power transmission apparatus and the like interposed between the first and second film feeding devices will cause some difference in speed between the two feeding devices even when a common driving motor is used for driving both the two devices. When two separate driving motors made according to the same standard are used one for the first film feeding device and another for the second one, it is very difficult practically to make equal the speed at which the first feeding device transports the film to the speed of the second one.
In case that the film transporting speed of the second one is lower than that of the first one, the length of film segment extending from the first feeding device to the second one is unduly increased to the extent that a jamming of the film may be caused and thereby the film may be bent and damaged. In such a case, the first and second film feeding devices can no longer operate properly.
On the contrary, if the film transporting speed of the second feeding device exceeds that of the first one excessively, the film will be subjected to an unduly large stretching force at the segment between the two feeding devices and the film portion lying at the opening for exposure of the cassette will be stretched at the time of exposure which in turn prevents image information from being recorded on the film exactly. In the worst case, there may occur damage and breaking of the film.
In order to avoid these troubles, it has been already known to provide a speed control device for sound motion picture cameras according to the prior art. The speed control device comprises a loop sensor for detecting the length of film segment extending between the two film feeding devices. When the film length is increased or decreased over or under a predetermined value of length, either one or both of the two film feeding devices are controlled to increase or decrease the film transporting speed so as to keep the length of the film segment almost constant. Sound motion picture cameras provided with such speed control device comprising a loop sensor are disclosed, for example, in U.S. Pat. No. T 920,009 (Defensive Publication), U.S. Pat. No. 4,003,643 and U.S. Pat. No. 4,000,496.
According to the prior art disclosed in the above-mentioned U.S. Pat. No. T 920,009 and U.S. Pat. No. 4,003,643, the first film feeding device is provided with a driving motor capable of being switched over from low speed to high speed or vice versa through a speed regulating circuit device. For the second film feeding device there is provided such driving motor which rotates at a substantially constant speed. A loop sensor senses the film segment between the two film feeding devices and controls the speed regulating circuit device according as the film length. When the length has become longer than a predetermined value, it is detected by the loop sensor and the speed of the driving motor for the first film feeding device is changed over to the low speed which is lower than the rotating speed of the driving motor for the second film feeding device. This changing-over of the motor speed is effected through the speed regulating circuit device. In a similar manner, when the length of the film segment existing between the two film feeding devices has become shorter than the predetermined value, the loop sensor detects it and changes over the driving motor for the first feeding device to the high speed condition through the speed regulating circuit device. The speed set for the high speed condition is higher than the rotating speed of the driving motor for the second film feeding device. Thus, the film length between the first and second film feeding devices is maintained at a certain given value.
In the arrangement disclosed in U.S. Pat. No. 4,000,496, the positional relation of the constant speed motor and the variable speed motor is reversed to that of the above described prior art. Namely, a driving motor rotating at a substantially constant speed is used for the first film feeding device and a driving motor the speed of which is changed over from a high speed to a low speed or vice versa through a speed regulating circuit device is used for the second one. The function of the speed control system disclosed in this U.S. Pat. No. 4,000,496 is entirely the same as that of the above described prior art. When the film length between the two feeding devices becomes too long, it is detected by a loop sensor and the speed of the driving motor for the second film feeding device is switched over through the speed regulating circuit device to the high speed that is higher than the rotating speed of the driving motor for the first feeding device. On the contrary, if the film length becomes too short, then the loop sensor detects it and the speed of the driving motor for the second film feeding device is switched over to the low speed which is lower than the rotating speed of the driving motor for the first one. Thus, like the cases of the above described prior art, the film length between the first and second film feeding devices is maintained almost constant at a predetermined value.
Speed control systems as disclosed in the above described U.S. Pat. No. T 920,009, U.S. Pat. Nos. 4,003,643 and 4,000,496 are all the same in the point that one driving motor provided for one of the two film feeding devices is changed in speed relative to another driving motor provided for the other one of the feeding devices so as to maintain substantially constant the film length extending between the two feeding devices. However, there is a possibility of such operational trouble that the film feeding device with a constant speed motor may stop transporting the film or the transportation of the film may become extraordinarily slow so that the other motor provided for the other film feeding device that is variable in speed gets out of control. If such trouble once occurred, the film would fall in jam between the two film feeding devices or the film would be subjected to an intolerably large tension stress. As a result, the film may be bent, damaged and broken. Also, the recording of image information or sound information on the film may result in failure.
All the prior art speed control systems described above have no means for preventing such possible trouble. They lack of safety of film and of recording the information. For the known sound motion picture cameras it is therefore required to take some measure with which safety of film and safe recording of information can be assured.